Mice have been used extensively to detect agents which might cause mutations in humans (human mutagens). Some mouse mutagen tests employ methodologies which can only be applied to mice, e.g., mouse specific-locus test. Other mouse mutagen tests use methodologies which may be applied to humans, e.g., sperm enzyme variants. We propose to develop and verify mouse mutagen tests of the latter type. In preliminary experiments we observed decreased sperm motility and acrosin activity (a protease enzyme located in the acrosome of the sperm) in animals in which spermatogonial cells were treated with the mutagen mitomycin C (MC). Decreased sperm motility has also been observed in F1 animals conceived from MC-treted fathers. In the proposed investigation we wish to (1) verify our preliminary finds with MC, (2) extend our investigation to the powerful mouse mutagen ethyl nitrosourea, and (3) develop one new single sperm enzyme assay. Such test systems, because of their applicability to humans, would be useful for detecting human mutagens.